Synergic Effect of the Mixed Cationic-Anionic Surfactants on the Interfacial Composition and Thermodynamics of W/O Microemulsions

The interfacial composition, the solubility of the alcohol in the oil phase, and the standard free energy change [image omitted] of transferring alcohol from the continuous oil phase to the interfacial layer in the W/O microemulsion stabilized by cationic-anionic surfactants sodium dodecyl sulfate and 1-hexadecyl-3-methylimidazolium bromide were studied with the dilution method. The synergic effect exists between cationic and anionic surfactants on the formation of W/O microemulsion. The effects of different alcohols, oils, and brine on the formation of W/O microemulsions stabilized by cationic-anionic surfactants were also investigated. The alcohols with longer chain length have higher efficiency to form the W/O microemulsion. Long-chain alcohol was easier to penetrate into the interfacial layer and less alcohol was needed to form the stable W/O microemulsion. The effects of decreasing the carbon chain length of the alkane molecules and increasing NaCl concentrations are equivalent to that of increasing the carbon chain length of the alcohol molecules.